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A079164 Twin-primorial numbers: running products of twin primes. 4
3, 15, 75, 525, 5775, 75075, 1276275, 24249225, 703227525, 21800053275, 893802184275, 38433493923825, 2267576141505675, 138322144631846175, 9820872268861078425, 716923675626858725025, 72409291238312731227525 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

The sum of the reciprocals converges to 0.4154254016622336549103692152614908366885449298862362851444631680740051..

LINKS

Table of n, a(n) for n=1..17.

EXAMPLE

The first two twin primes are 3 and 5, so the first term is 3 and the second term is 15.  The next two twin primes are 5 and 7, so the third term is 5*15=75 and the fourth term is 75*7=525

MATHEMATICA

Rest[FoldList[Times, 1, Flatten[Select[Partition[Prime[Range[30]], 2, 1], Last[#]-First[#]==2&]]]] (* Harvey P. Dale, Mar 16 2011 *)

PROG

(PARI) twprfact(n) = {sr=0; tp = vector(10000); k=1; forprime(j = 3, n, if(nextprime(j+1)-j == 2, tp[k] = j; tp[k+1] = j+2; k+=2; ); ); for(j=1, k-1, y=1; for(i = 1, j, y*=tp[i]; ); print1(y", "); sr+=1.0/y; ); print(); print(sr); }

CROSSREFS

Sequence in context: A000266 A294340 A059838 * A240941 A047015 A322186

Adjacent sequences:  A079161 A079162 A079163 * A079165 A079166 A079167

KEYWORD

nonn

AUTHOR

Cino Hilliard, Feb 03 2003

EXTENSIONS

Definition clarified and example provided by Harvey P. Dale, Mar 16 2011.

STATUS

approved

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Last modified August 10 06:08 EDT 2022. Contains 356029 sequences. (Running on oeis4.)